1. Field of the Invention
The present invention relates generally to a wafer stocker. In particular, the present invention relates to a wafer stocker with an embedded storage shelf.
2. Description of the Prior Art
With the development of semiconductor process steps to very-large-scale integration (VLSI), the manufacture of integrated circuit becomes more complicated and difficult. It may need hundreds of processes to manufacture a circuit with high integrated density. The complicated processes will increase the complexity and impact the flexibility for WIP (Wafer-In- Process) dispatching and allocation. The wafers or pods in process are frequently moved between bays or process tools in the FAB depending on their current process step. Also, the wafers may be pended in current stage and be stopped in the planned course of the wafer fabrication flow because of capacity planning or unexpected inline issues. To respond to the above-mentioned situations, the wafer stocker is used as an equipment to temporarily store the wafers and provide a function of wafer transferring. The wafer stocker may be associated with an automatic material handling system (AMHS) to adjust the WIP according to the production line factors, such as process capability, tool layout, process planning, or alarm situation, in order to effectively improve the capacity utilization of the process tools.
Wafer stockers are usually disposed at each bay in the clean room of the FAB, which capacity depends on the requirement of each bay. In addition to the function of wafer storage, the wafer stocker may also be regarded as a transportation medium in each bay. The wafer pod (or FOUP) is transported via the wafer stocker to the next predetermined process tool or bay after completing the current process.
The number of wafer stockers and their storage cells primarily depends on the scale of the FAB and the design of the production line. The number and the position of each wafer stocker should be adapted to the tool group in each bay and the AMHS in order to obtain the most efficient configuration. Furthermore, the wafer stocker in nowadays 12-inch wafer FAB is usually provided with an additional wafer sorter to perform a pod splitting/merging step. The number and capability of the wafer sorter has a significant influence on the process performances. It is necessary to add or remove the wafer sorter from the wafer stocker according to the changes in process capability, tool distribution or process planning.
Accordingly, in order to install wafer sorters in wafer stockers, the conventional approach is to make some room in the wafer stocker to accommodate the wafer sorter. This space will be reserved until the wafer sorter needs to be installed. For this kind of conventional method, the reservation of the accommodation space is undoubtedly a waste of the space in wafer stocker. Moreover, the above-mentioned conventional installation method is labor-cost work and quite time-consuming, which can't therefore meet the requirement of high capacity utilization of nowadays wafer FAB and Cost Management.